Detecting events occurring on remote telephone

ABSTRACT

A process and a system are disclosed for detecting activity, e.g., three way calling, call forwarding, or the like, during a phone call. The process includes, and the system is configured for, establishing the call path between a first party and a second party, adding a reference tone to the call path, observing a reflected tone from the call path, and determining a relationship between the reference tone and the reflected tone. Information relating to the relationship may be reported for further analysis.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 11/283,559, filed on Nov. 17, 2005,entitled “Phase Change,” which is incorporated by reference herein inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the field of telephonesystems, and more specifically, to activity detection mechanisms intelephone systems.

2. Description of the Related Art

Subject to state Public Utility Commission regulations, ownership ofCustomer Owned Coin Operated Telephone (COCOT) service is permitted. Anoutgrowth of COCOT service has been the private operation ofinstitutional telephone services. However, “privatization” of phonesystems has created a number of technical challenges. Examples ofchallenges include automated detection of a called party's response tosome appropriate prompt (such as, a request for acceptance of a collectcall) by dialing a pulse-dial telephone and, in the case of prisonsystems, the prevention of three-way calling.

Coin telephones owned by local telephone companies generally utilizedirect current (DC) signals to signal called-party-answer. Thisinformation is transmitted between telephone company central offices andthen to the originating pay telephone telling it, in effect, to acceptpayment for the call. This information is not normally communicated toconventional, i.e., regular business and residential, telephones. Undersome tariffs, some, but not all, of this information may be available toCOCOT equipment.

Collect calls placed through COCOT equipment are typically handled by anautomated operator service (AOS), thus providing the owner of the COCOTequipment with the ability to provide collect call service and billusers of that service for both intra- and inter-local access andtransport area (LATA) calls. However, the use of an AOS for collectcalls is expensive. In addition, in certain instances, there remains apossibility of fraudulent activity.

In many institutions the phone calls placed by a patient/client orprison inmate are primarily, if not exclusively, collect calls. Collectcalls initiated by a patient/client must be indicated as such to thecalled party. In addition, calls placed by an inmate to an outside partyoften begin with a prerecorded message stating that the call or collectcall is from “a prison” and is being placed by “prisoner's name.” In theabove cases the called party is usually asked to dial a digit, commonlya “0” or a “1”, to accept the call or the attendant charges. The phonesystem providing such service must be able to detect such acceptanceboth as a dual-tone-multi-frequency (DTMF) tone response from a“touch-tone” phone as well as to detect the equivalent response on apulse-dial telephone.

The clients/inmates in some institutions may be allowed to call onlynumbers on a pre-authorized list in order to deter fraudulent activity.Thus, a prison phone system, for example, must be able to detect thecalled party's flashing the hook switch in order to prevent the calledparty from activating three-way (i.e., conference) calling, dialinganother number and then connecting the prisoner to an unauthorized phonenumber.

To address the problems described, conventional telephone call handlingequipment automatically route local and long distant calls without theintervention of an outside service or live operator. This enables thetelephone owner/service provider to charge for the completion of a callor collect call while providing an opportunity to prevent certain calls,e.g., three-way calling. To do this, such conventional systems wereconfigured to detect “hook-flash” conditions, of which several methodsof detecting a three-way call initiated by a hook-flash were known inthe prior art.

The hook-flash results in a temporary disconnect and reconnect which canbe observed as a momentary interruption of loop current at the telephonecompany central office. The loop current loss, however, is not observedelsewhere in the network nor is the loop current loss made known to therespective parties. Thus, this attribute of a hook-flash is onlyemployed at the central office.

In addition, conventional approaches for detecting initiation of athree-way call have been disclosed in U.S. Pat. No. 5,319,702 (the '702patent) and U.S. Pat. No. 5,539,812 (the '812 patent). The systemdisclosed in the '702 patent is based on analog technology andaccurately detects a vast majority of attempted three-way calls. Thesystem disclosed in the '812 patent is based on the detection ofadditional characteristics of the hook-flash signal and utilizes digitalsignal processing (DSP). The system disclosed in the '812 patentgenerally is more discerning of the attempted three-way call as well asfurther equipped to distinguish an attempted three-way call from otherevents that occur on the telephone line (such as, voice fluctuations,noises from physical contact, e.g. dropping or tapping, of the handset,etc.).

Yet another approach to three-way call detection was disclosed in U.S.Pat. No. 5,768,355 (the '355 patent). The system disclosed in the '355patent established a baseline ambient, or background, noise level, anddetected when the signal noise level dropped below the ambient noiselevel. When the current signal noise level dropped below the ambientnoise level, the system assumed that the called party attempted athree-way conference call.

A problem, however, with this approach is that the ambient noise levelduring the call may change, which in turn, triggers the particularmethodology resulting in a disconnected call. For example, consider aninmate placing a call from a prison phone system. This call is picked upby a person on the receiving end. If that person places the receiverdown, e.g., to close a door, there may be a change in the ambient noiselevel, which results in a disconnected call. The problem is furtherexacerbated by the fact that re-establishing a call results in anotherconnect charge or may result in the caller, i.e., the inmate, beingprohibited from making any further calls for at least a specifiedperiod, e.g., one week, based on the phone system configuration andcaller profile.

In addition, U.S. Pat. No. 5,504,810 (the '810 patent) discloses atelecommunications network using quasi-time domain reflectometrytechniques to identify those telephone calls, which comprise multiplelegs. Echo data is collected for the telephone call from a predeterminedpoint in the network to a point where the call originated. The data isprocessed to generate an indication of whether the telephone callcomprises multiple legs, thus identifying those calls most susceptibleto unauthorized use. The indication that a telephone call comprisesmultiple legs is used together with call attribute information, such aswhether the call is placed to an international destination, to determinewhether a given multiple-leg call is a valid access to the communicationsystem or potentially fraudulent.

However, a problem with this approach is that the '810 patent disclosesa method to potentially detect fraudulent access to a telecommunicationsystem. This method can be applied to detect unauthorized access to(ingress) the system from a point other than the point identified as anotherwise legitimate access point. This method provides no means todetect changes in call paths, particularly at the called party end, oncethe call has been established.

Hence, in view of the above, there is a need for a system and a processto detect and analyze particular signal characteristics that associatewith particular activity within an established call in a telephonesystem so that subsequent analysis on those characteristics allows forevaluating whether an activity beyond the established call has takenplace.

SUMMARY OF THE INVENTION

The present invention includes a process and a system for monitoring atelephone call between an A-party and a B-party to determine whetherparticular activity, e.g., three-way calling, or the like, has occurredduring the present call. By way of example, in a conversation between anA-party and a B-party, the B-party may try establishing a three-way callwith a C-party (third-party). The process and system are configured todetect and report such activity.

The process and the system are integrated in a communication system thatincludes the A-party, a detection system, a telecommunication system,the B-party, and optionally the C-party. The telecommunication systemmay be a public switched telephone network (PSTN), a private branchexchange (PBX) system, a voice-over Internet Protocol (VoIP) system, acellular communication system, or the like.

In one embodiment the process (or appropriately configured system)includes establishing the call path between a first party and a secondparty, adding a reference tone to the call path, observing a reflectedtone from the call path, and determining a relationship between thereference tone and the reflected tone. Information relating to therelationship may be reported for further analysis.

More particularly, the process (or appropriately configured system) mapsthe reference tone and summed reflected tones to the time domain.Thereafter, the process starts a timer at, for example, a negative goingzero crossing of the reference tone and stops the timer at, for example,a negative going zero crossing of the summed reflected tone. The processthen calculates a time difference with this data to provide theinformation on relationship between the reference tone and the reflectedtone. The time difference information can then be treated as a phaseindicator even though the information does not, and need not, representany actual phase relationship between the reference tone and the summedreflected tone. Information relating to the phase indicator may then beanalyzed to determine “abnormal” activity in an established call path.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be morereadily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIGS. 1 a through 1 d illustrate embodiments of a telephonecommunication system in accordance with the present invention.

FIG. 1 e illustrates an embodiment a communication system overview inaccordance with the present invention.

FIG. 1 f illustrates one embodiment of a detection system in accordancewith the present invention.

FIG. 2 illustrates one embodiment of a process for monitoring acommunication system for a characteristic changes in a call path inaccordance with the present invention.

FIGS. 3 and 4 illustrate embodiments for processes to determinerelationships between a reference tone and a reflected tone inaccordance with the present invention.

FIG. 5 illustrates one embodiment of a process for determining asignificant phase change in a system in accordance with the presentinvention.

FIGS. 6 a through 6 c illustrate waveforms for use in a single ormulti-tone configuration for monitoring a communication system for acharacteristic changes in a call path in accordance with the presentinvention.

FIGS. 7 a through 7 c illustrate waveforms for use in a dual toneconfiguration and perception of the tones by a human ear in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Figures and the following description relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that from the following discussion, alternativeembodiments of the structures and methods disclosed herein will bereadily recognized as viable alternatives that may be employed withoutdeparting from the principles of the claimed invention.

Reference will now be made in detail to several embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict embodiments of thepresent invention for purposes of illustration only. One skilled in theart will readily recognize from the following description thatalternative embodiments of the structures and methods illustrated hereinmay be employed without departing from the principles of the inventiondescribed herein.

In addition, the present invention is particularly suited for telephonesystems used in environments such as public or private pay phones,prison systems, or other telephone systems that could be monitored todetect call path activities such as third-party calling and the like.Moreover, the present invention is configurable to adapt to conventionalsystem such as those referenced in U.S. Pat. No. 5,319,702 (the '702patent), and U.S. Pat. No. 5,539,812 (the '812 patent), the relevantportions of which are herein incorporated by reference.

By way of example, FIGS. 1 a through 1 d illustrate embodiments of atelephone communication system in accordance with the present invention.The telephone communication system includes an A-party telephone 110 (orsimply A-party 110) and a B-party telephone 120 (or simply B-party 120)that are interconnected through a public switch telephone network(PSTN).

In FIGS. 1 a and 1 b, the A-party 110 communicatively couples with ananalog station interface (ASI) 102, which communicatively couples withcustomer premise equipment 104. The customer premise equipment (CPE) 104communicatively couples with an analog trunk interface (ATI) 106. TheATI 106 communicatively couples with the public switched telephonenetwork (PSTN), which includes a class 5 central office, (generally108). The PSTN 108 includes subscriber line interface circuits (SLICs)and an analog or digital switching matrix that interconnects appropriateSLICs. The B-party 120 communicatively couples a SLIC in the PSTN 108.In FIG. 1 a the PSTN 108 includes a switch fabric and in FIG. 1 b thePSTN 108 b includes a TDM matrix fabric.

It is noted that the customer premise equipment 104 includes one or morenotch filters 104 a, one or more reference tone generators 104 b, asummation module (or circuit) 104 c, one or more band pass (BP) filters104 d, a detection module 104 e, and a summation module (or circuit) 104f. The notch filters 104 a are coupled in series. Specifically, a firstnotch filter 104 a 1 communicatively couples with the ASI 102 to receivemicrophone signals from the A-party telephone 110 (which are earpiecesignals for the B-party 120). The first notch filter 104 a 1 filters thesignal (e.g., filters a first frequency) and passes it on to a secondnotch filter 104 a 2. The second notch filter 104 a 2 further filtersthe signal (e.g., filters a second frequency) and forwards the signal tothe summation module 104 c. The summation module 104 c iscommunicatively couples the one or more reference tone generators 104 b.The summation module 104 c is also communicatively couples with the ATI106. In particular, the summation module 104 c is configured to sum thesignals from the notch filters 104 a 2 with reference tones from the oneor more reference tone generators 104 b and forward them to the ATI 106.

The customer premise equipment 104 also is configured to receive signalsfrom the ATI 106 that originated from the B-party telephone 120.Specifically, the ATI 106 transmits the signals (which are microphonesignals from the B-party 120) to the ASI 102 (which become earpiecesignals for the A-party 110). This signal is tapped by the one or moreband pass filters 104 d and sent to the summation module 104 f to sumthe signal to the detection module 104 e.

Those skilled in the art will appreciate that the summation module 104 fcan be implemented as shown in dual-frequency reference toneconfigurations. This is so that the detection module 104 e can bepresented with a composite reflected tone set similar to the compositetone set 705. Likewise, those skilled in the art will recognize that thefunction of the summation module 104 f could also be computationallyimplemented within the detection module 104 e. Thus, in dual frequencyimplementations, the detection module 104 e would be able to observe andmake decisions based upon characteristics of the entire envelope of thereflected tones as well as the characteristics of the individual tonecomponents. It also is noted that operations of detection module iffurther described below with respect to single tone and multi-tonefunctional overviews.

Note that the path from the ATI (microphone signal path from B-party)106 to the ASI (earpiece signal path for A-party) 102 may also include aset of one or more notch filters. In one embodiment, the one or morenotch filters can be placed above the taps providing the B-partymicrophone signal to the inputs of the band pass filters. In thisconfiguration the A-party will most likely not hear any reference orreflected tones. Likewise, although the B-Party may, at least briefly,notice the tone or tones (despite selection as non-intrusive tones), andmay even mention “I think I hear a tone” to the A-Party (e.g., inmate)both parties may well assume that the tone heard by the B-party existsonly on the B-party side, therefore interpreting the tone as beinginsignificant.

It is noted that in one embodiment, the notch filters 104 h may beconfigured so that a first notch filter 104 h 1 communicatively couplesthe ATI 106 to receive and filter (e.g., filter a first frequency) aB-party microphone signal. A second notch filter 104 h 2 receives thefiltered signal and filters it again (e.g., filter a second frequency)before passing the signal to the ASI 102 as an A-party earpiece signalfor the A-party telephone 110.

In addition, the reference tone level, as perceived by the B-Party areat least 6 dBm lower level than at the point of generation (referencetone generator 104 b) due to the expected termination loss of theterminating central offices 108, 109 this further minimizes thedetection of the reference tone or tones by the parties to the call. Asfor the one or more notch filters in this configuration, in oneembodiment they would be configured for the same frequencies as the oneor more notch filters 104 a. The actual level of attenuation may be lessstringent for the additional set of notch filters due to the lossesalready incurred in the process of passing through the system from thegenerators to the B-Party and back again. Thus, in some embodiments thissecond set of notch filters could be computationally “cheaper” orprogrammatically identical to 104 a thus incurring minimal additionalcode.

It is noted that in another alternative embodiment, a phase lock loop(PLL) 104 g can be added after each band pass filter 104 d, prior tosumming the signal in the summation module 104 f. These configurationsare illustrated in FIG. 1 d. In such embodiments, an appropriatelyconfigured phase lock loop (e.g., comprised of a gain-controlled PLLimplementation) may allow for use of lower reference tone levels.

The controlled gain PLL may be implemented by a specific pair of twodifferent types of PLL's for each test tone frequency being used in theoverall system. In each PLL pair the “front” (preliminary) PLL has arelatively wide capture range but has a very tightly controlled outputlevel for the signals that meet its capture criteria, while the “rear”(primary) PLL has a very narrow capture range to eliminate all but thespecific frequency (for that PLL pair) of interest. A characteristic ofnarrow band PLL's is their requirement for a very fixed input level inorder to provide the desired accuracy. Thus, the attendant requirementfor the preconditioning PLL in front of the final discriminator PLL. Itis noted that alternatively the PLL functions may be provided by digitalfunctional equivalent, e.g., hardware DSP, or other logicalimplementations.

Referring next to FIG. 1 c, it illustrates an alternative configurationof a conventional telephone system in which both the A-party 110 sideand the B-party 120 side, relative to a PSTN 101, include a centraloffice 107, 109. Each central office 107, 109 includes switching fabricthat communicatively couple through the PSTN 101. The ATI 106 on theA-party side couples a SLIC in the central office 107 on its side andthe B-party 120 couples a SLIC in the central office 109 on its side.

It is noted that the configuration of the customer premise equipment 104illustrated in FIGS. 1 a through 1 d beneficially addresses problems ofconventional customer premise equipment configurations. Specifically,conventional customer premise equipment configurations use band passfilters rather than notch filters for the A-party telephone 110microphone signal path. The problem with such conventionalconfigurations is that some voices transmitted through the A-partytelephone 110 are almost entirely low frequency with relatively few highfrequency components. Hence, a person at the B-party telephone 120 oftenhas trouble hearing the voice and may be tempted to talk even louderthinking there is a bad connection. The problem is further exacerbatedas the person at the A-party telephone 110 may then tend to speak evensofter because they think that they may be talking too loudly hearingthe raised voice from the B-party telephone 120.

To address this issue with conventional customer premise equipment, inone embodiment of the present invention, the customer premise equipment104 is configured to include one or more notch filters 104 a in themicrophone signal path between the A-party telephone 110 and the B-partytelephone 120. In particular, the customer premise equipment uses areference tone generator 104 b, which allows the notch filters 104 a toisolate a particular and narrower range of frequencies for observation(and filtering). Specifically, one embodiment of the present inventionis configured to identify characteristic reflections of a particularfrequency that can be filtered through the notch filters rather than abroad range of frequencies that a high pass filter is configured toobserve (and filter). In turn, this configuration reduces the ability ofan A-party telephone 110 user (e.g., the calling party) to interferewith a detection process, for example, a detection process as outlinedherein.

Referring to FIGS. 1 a through 1 d in general, those skilled in the artwill understand that while the telephones 110, 120, and interfaceequipment 102, 106 are shown as analog equipment, these components maybe of any technology appropriate for voice telecommunications. Similarlywhile the processing, switching, filtering, and detection equipment 104is typically digitally implemented these functions may likewise beperformed by any appropriate technology.

It also will be understood by those skilled in the art that therelationship depicted in FIGS. 1 a through 1 d is the interconnection ofthe elements and that the specific physical location of the elements isnot a requirement for proper application of the teachings. For example,in FIG. 1 c, the overall functions of elements 102, 104, 106 need not belocated physically near telephone 110 in the traditional customerpremise equipment arrangement. It is only required that the logicalconnection arrangement be preserved. For example, the addition ofadditional transport means between telephone 110 and an appropriatestation interface 102 would permit the elements 102, 104, 106 tophysically remote from telephone 110 without changing the functionaloperation of the system.

Note that interfaces 102, 106 need not be analog nor do they necessarilyneed to be time division multiplexed (TDM) because any portion of thesystem prior to the transport mechanism towards the B-Party 120, e.g.,106, 107, 101, is not necessary for the principles of the presentinvention to continue to be operable. Hence, the principles disclosedherein would be applicable to systems in which a different transportmechanism is used in place of, e.g., 106, 107, 101, for example in voiceover packet or VoIP systems.

Monitoring System Architectural Overview

FIG. 1 e illustrates an embodiment of a monitoring system (and aprocess) for use in a communication system 101 in accordance with thepresent invention. Specifically, the monitoring system monitors atelephone call between the A-party 110 and the B-party 120 to determinewhether a non-authorized activity has occurred during the telephone callbetween the party, for example, establishing a three-way call with aC-party (or third-party) 130.

In one embodiment, the monitoring system is configured for integrationwithin or with the communication system 101. The communication systemincludes the A-party 110, a detection system 115, a telecommunicationsystem 150, the B-party 120, and optionally the C-party 130. An exampleof a telecommunication system includes the PSTN 101 or a voice overpacket-type system. In addition, the telecommunications system may beconfigured to operate within a private branch exchange (PBX), a voiceover packet, a cellular communication environment, a combination ofthese or the like. In one embodiment, the detection system 115 may beconfigured within the customer premise equipment 104 on the A-party 110side. Alternatively, the detection system 115 may be configured apartfrom customer premise equipment 104, although communicatively coupled toit.

FIG. 1 f illustrates an embodiment of the detection system 115 inaccordance with the present invention. The detection system 115 includesa call establishment module 152, a tone generator 154, an observationmodule 156, one or more notch filters 158, a signal character module160, relationship module 162, a timer 164, a statistical analysis module166, and report generator 168. Each module/component is coupled througha system processing core 170, which includes a processor and/orcontroller and other components necessary for the detection system 115to function as described herein. It is noted that the detection system115 may be configured in software, in hardware, or a combination ofsoftware and hardware in a manner that achieves the functionality asdescribed herein.

Functional Overview—Single Tone

FIG. 2 illustrates one embodiment of a process for monitoring acommunication system for a characteristic changes in a call path inaccordance with the present invention. Operationally, the process starts210 and the A-party 110 goes off hook 215. The call establishment module152 places a call through the telecommunications system (e.g., PSTN 101)to the B-party 120 to establish a call path 220.

Once the call reaches steady state 225 (e.g., established), the tonegenerator 154 adds a tone 230 in the call path from A-party to B-party.This tone may be referred to as a reference tone. A frequency of thereference tone may be predetermined, e.g., hard-coded, into the systemor may be configurable, e.g., set by a user in hardware and/or software.Note that the tone is preferably selected to be non-intrusive andprovides a reference in the direction from the A-party towards theB-party.

The tone may be a single tone or multi-tone. For a single tone, itsfrequency is preferably the lowest frequency that can be transmittedalong the call path without significant attenuation. The single tone isalso selected to be within a communication channel pass band. Lower tonefrequencies, which are often within the frequency range of the humanvoice, are preferred over higher tones frequencies because lower tonesfrequencies generally are not intrusive within the minds of prospectivecallers. In addition to non-intrusiveness, lower tone frequencies, e.g.,200 Hertz (Hz) or 300 Hz, also offer advantages of higher (greater)resolution for signal analysis than higher tone frequencies, e.g., 3000Hz or 3500 Hz. This higher resolution is due to a greater relativesampling rate available at lower frequencies as compared with the higherfrequencies, with the common telecommunications sampling rate of 8kilosamples per second.

With respect to an audio “level” (e.g., volume/power) of the referencetone(s), i.e., how “loud” the reference tone may be, it is noted that inone embodiment reference tone levels are on the order of −20 to −35dBm0. In some embodiments, a preferred embodiment level may beapproximately −30 dBm0 for at least a single frequency reference tone orthe higher frequency tone of a dual or multiple frequency tone set. Inembodiments involving a dual frequency reference tone, a level of thelower frequency tone can be selected, along with its frequency, whichadvantageously masks a perception of the tones by the participants onthe call.

Upon reaching steady state 225 and adding the reference tone 230 intothe call path, e.g., when no caller is speaking, and therefore with nointerferences, the observation module 156 in the detection system 115observes reflected tones 235 (e.g., due to impedance changes along thecall path and reflections from the B-party 120). Referring briefly toFIG. 3, to observe the reflected tones, a sub-process starts 310 withone or more band pass and optional notch filters 158 in the detectionsystem 115 filtering the reflected tones 315 to remove influences fromvarious components within the call path, e.g., speech and backgroundaudio at the telephone of each party. As the reflected tones arefiltered, the signal character module 160, along with the inherentaction of the communications network, sums the reflected tones 320 toprovide a composite reflected tone.

The reflected tones are primarily from reflections at points of hybridswithin a telephone communication system. The reflected composite signalhas the same (or substantially the same) frequency components as thereference tone frequency components, although the individual reflectedtones may have different phases. The detection system, e.g., observationmodule 156 and/or the signal characterization module 160, is furtherconfigured to observe and identify a particular tone characteristic (ortrait) sought to be observed, e.g., a zero crossing for the compositereflected tone. This tone characteristic, e.g., zero crossing point,provides a static reference point from which changes in a tone can beobserved as further described herein. Alternatively, the detectionsystem can be configured to use other tone characteristics, e.g.,inflection point, a waveform peak magnitude or waveform valleymagnitude, as a static reference point to observe changes.

Turning back to FIG. 2, the relationship module 162 determines arelationship between the phase of the composite reflected tone with thatof the reference tone, e.g., a phase indicator. Specifically, therelationship module 162 is configured to evaluate a time differencebetween the reference tone and the composite reflected tone. FIG. 4illustrates an embodiment for this process.

Referring to FIG. 4, the process starts 410 and initially the frequencyof the reference tone is mapped to a time domain 415 to determine itsperiod so that, for example, a 200 Hz reference tone, would have betweenits similar zero crossings a time difference of 5 milliseconds (5milliseconds using t=1/f). The composite reflected tone is also mappedto a time domain 420, but the mapping also takes into account theappropriate phase indicator, e.g., between 0 degrees (right on apparentphase) to almost back to zero (at just before 360 degrees). Thoseskilled in the art will appreciate that this phase difference indicatormay not, and need not, accurately represent any actual time delay orphase shifts in the overall system, e.g., the system as illustrated inFIG. 1 a.

With the reference tone and the reflected composite tone mapped to atime domain, the system begins to make a finite period of measurementbased on the frequency in use. Specifically, the timer is started (ortriggered) when a reference tone is for example, negative going at azero crossing 425 and is stopped when a reflected composite tone is, forexample, negative (or positive) going 430. The start and stop values maybe stored in a state machine, a register, a memory, a storage device(e.g., optical, solid-state, or magnetic drive), or other storagemechanism. The statistical analysis module 166 uses the start and stoptimes to calculate a phase indicator 435 between the reference tone andthe reflected composite tone.

Turning back to FIG. 2, over some set or predefined period of time dataregarding this phase indicator is gathered and reported 245, e.g., bythe report generator to a screen or to the storage mechanism. As phaseindicator data is continually gathered, it may be stored and furtherused for additional analysis such as determining when there are“disturbances,” e.g., phase difference using the gathered phaseindicator data, further analysis may be done to calculate mean or medianphase indicator values, which can then be used to evaluate relevantaberrations versus momentary aberrations in activity along the callpath, e.g., as caused by components of the B-Partys voice that happen tocoincide with similar components of the reference tone or tones.

FIG. 5 illustrates one embodiment of a process for determining asignificant phase change in a system in accordance with the presentinvention. The process starts 510 and obtains 515 a current value of aphase indicator. The process then compares 520 the current value of thephase indicator with a reference phase indicator. In one embodiment, thereference phase indicator may be a previous phase indicator relative tothe current (or present) phase indicator.

Next, the process determines 525 if there is a significant change inphase indicator value as a result of the comparison. If not, the processupdates 530 the reference phase indicators. If so, the process retrieves535 data associated with this change for further action before ending540. The further action may be, for example, an automated action to cutoff a call or a request for manual action such as an inquiry of whetherto cut off a call. In addition, it is noted that the process may beconfigured as a looping process.

In one embodiment, the present invention advantageously exploits aconventional 8000 Hz clock rate to implement a timer. As an example theabove process can be described as described herein using a 250 Hzreference tone and an 8 kilosample per second sampling rate, whichprovides a scale of 32 points. The scale factor of 32 in this case isderived by dividing the sample rate by the reference tone frequency,e.g., 8000 Hz/250 Hz yields 32 possible values for the phase indicator(it is noted that this scale of 32 means that if the timer is clocked atthe 8 kilosample clock rate the resulting phase indicator can have anyof 32 integer values, in this case from 0 to 31 or from 1 to 32,depending upon how the timer start and stop mechanisms are implemented).Thus, the values of the phase indicator received are between 0 to 31 or1 and 32, inclusive. It is noted that the principles of the presentinvention are also applicable with other clock rates.

In one embodiment an averaging algorithm is used to obtain a phaseindicator value, e.g., a review of a sequence of readings over apredetermined period of time, such as 10 readings per second. As thephase indicator values are obtained (or received) by the system (e.g.,of FIG. 1 f), the values are checked to determine if a significantchange has occurred relative to prior values. For example, if the phaseindicator values are averaging 19, 19, 19, 19, 18, 19, 19, 18 and thensuddenly go to an average of 14, 13, 14, 13, 14, 14 over a period oftime, this may be construed (e.g., by predetermined configuration) bythe system to be a significant change in value. In such instances, thesystem may be configured to take an automated or manual next step aspreviously described.

Functional Overview—Multi-Tone

The system and process described to this point are also applicable foruse in a multi-tone configuration. FIGS. 6 a through 6 c illustratewaveforms for use in a multi-tone configuration for monitoring acommunication system for a characteristic changes in a call path inaccordance with the present invention. By way of example, the multi-toneconcept is illustrated through use of two single tones, one at 350 Hzand the other at 440 Hz, which are shown in FIGS. 6 a and 6 b,respectively. FIG. 6 c illustrates the sum of the first single tone,e.g., at 350 Hz, and the second single tone, e.g., at 440 Hz, thatproduces a “dual tone” (i.e., two tones).

A purpose of the second single tone is twofold. A first purpose is tosomewhat “mask” the first single tone so that neither the A-party 110nor the B-party 120 perceives either tone in the course of theirconversation. Although this example uses frequencies of 350 Hz and 440Hz, any two frequencies for the tones may be selected so that inclusionof the two single tones in a call path is relatively non-intrusive tothe callers, i.e., do not interfere with conversation and, thus, shouldbe unnoticed by the parties.

Those skilled in the art will recognize that the resulting “differencetone”, or beat frequency, will tend to dominate the callers subconsciousattention as being non-interfering due to its low apparent frequency andthat the single tone frequencies, and thus the difference frequency, maybe selected to tend to mask the perception of the higher frequencysingle-tone signals and further tends to particularly mask the higherfrequency single tone signal which could otherwise be the more intrusivesignal as perceived by the callers (parties 110, 120).

A second purpose of the second single tone is to provide an overalllonger time period over which the combined dual-tone waveform repeats.An example would be to use the single tone frequencies of 160 Hz and 200Hz resulting in a beat/difference frequency of 40 Hz. Thus, whileassuming the same 8000 samples per second the 160 Hz single tone wouldprovide a scale of 50 points, and the 200 Hz single tone would provide ascale of 40 points but the combined dual-tone waveform provides a scaleof 200 points. Stated differently, the case of a single 160 Hz referencetone would provide a resolution of one part in 50 or two percent.Likewise, the case of a single 200 Hz reference tone would provide aresolution of one part in 40 or two point five percent. But theresolution of the combined dual tone pair is one part in 200 or one-halfpercent.

FIGS. 7 a through 7 c illustrate the “mask” concept using the firstsingle tone of 350 Hz (shown in FIG. 7 a) and the second single tone of440 Hz (shown in FIG. 7 c) as an example. Specifically, FIG. 7 cillustrates what is the “perceived” tone from the perspective of theA-party 110 and the B-party 120.

Thus, from the perspective of monitoring the call path between theA-party 110 and the B-party 120, the perceived tone resulting from eachsingle tone, e.g., 350 Hz and 440 Hz, provides an opportunity to observeparticular signal characteristic such as inflection points, which arepoints at which there is a change in direction of a signal (e.g.,positive going to negative going and vice versa). One example of aninflection point is a “tips” 710. In FIG. 7 c, the tips 710 provide auniquely identifiable characteristic of the waveform, which may be usedto further analyze signal characteristics. For example, the tips 710 canbe used in addition to, in lieu of, or in combination with the zerocrossing data described previously to analyze and/or report aboutactivity along the call path between the parties 110, 120.

In an alternative embodiment, an envelope 705 of the combined reflectedtones resulting from the dual reference tones can be used for furtheranalysis of signal characteristics. For example, referring again to FIG.7 c, reference point 715 illustrates a minimum of the envelope 705 whilereference point 725 illustrates a maximum of the envelope. In oneembodiment, the system can be configured to identify such points forappropriate analysis in determining changes in call characteristics.

It is noted that in some embodiments in accordance with the presentinvention, once a “characteristic” is selected than that characteristicof the reference tone or combined/composite reference tone would be usedto start the timer and any appropriate characteristic of the reflectedtone or composite reflected tone, consistent with the selectedcharacteristic of the reference tone, would/could be used to stop thetimer, e.g., a zero crossing near the minimum envelope of the combinedreference tone could be used to start the timer and a “tip”/peak point(inflection point) of the combined/composite reflected tone could beused to stop the timer.

In addition, if a currently selected combination of characteristicsbeing used to start and stop the timer “causes trouble,” e.g., causesreadings that fluctuate between “minimum scale” and “maximum scale”(e.g., an apparent “0” phase indicator) then the system couldbeneficially change to a different combination of characteristics inorder to obtain timer readings somewhere else on its available scale ofvalues. Thus, the “resulting phase indicator” need not bear anyresemblance to an actual “phase measurement.”

In addition, embodiments can be configured that allow for purelycomputational means to compensate for a selected combination ofcharacteristics (to start and stop the timer) that “cause trouble,”e.g., adding a fixed offset to all timer readings resulting in an“offset scale.” Such embodiments can be employed advantageously, even ifthey may not be in the “range” of the scale provided by a raw timerbased upon the sampling rate and selected tone/composite tone overallrepetition rate.

Moreover, embodiments can be configured that allow for computationalmeans to compensate for a selected combination of characteristics (tostart and stop a timer) that “cause trouble,” e.g., modulo addition of afixed offset to all timer readings where the modulus is the samenumerical value as that of the scale length as described previously asappropriate for the particular embodiment. An example would be a scalelength of 32 where a sequence of timer readings such as 32, 1, 1, 32,31, 32, 1, 32 appears to be troublesome for simple subtraction to seethe true nature of the sequence. However, adding some fixed value, wherethe actual value added is arbitrary, modulo 32 (in this example)clarifies the situation. In another example, adding the offset value of5, modulo 32, to the example sequence results in the clarified sequenceof values 5, 6, 6, 5, 4, 5, 6, 5.

The present invention advantageously provides a system and a method todetect activity along a call path, e.g., hook-flash to incorporate aC-party 115 in a call between an A-party 110 and a B-party 120. Byobserving and monitoring one or more reference tones along a call path,the system and the method beneficially can track, monitor, and reportactivity along a call path without being intrusive to parties along acall path. Moreover, most callers would be unlikely to detect themonitoring activity through the disclosed embodiments. Hence, thepresent invention provides monitoring and reporting security thatprevents calling parties from engaging in opportunities to bypass suchdetection.

It is noted that in general each of the reference tone frequencies, andthus the reflected tone frequencies, can be within the frequency rangelimited by a lowest frequency that the telecommunications systems willpass without significant degradation, as well as the “low” end ofprimary communication/speech energy frequencies. In many systems, forexample, in many non-U.S. countries, the low end of an “official”telecommunications network is defined to be 200 Hz. Lower frequencyenergy will still be carried, although there may be some impairment. Inother systems, for example, many systems in the U.S., the official lowend is defined to be 300 Hz, although in practice the low end frequencycapability of the U.S. network actually is similar to the rest of theworld.

The upper, but relatively low, frequency limit may be chosen with morepractical view. In one embodiment, a frequency is selected that is notthe same as those considered important carriers of speech information asthat frequency (or frequencies) may be removed through the notchfilter(s). For example, customer/user signaling frequency pairs may beas follows:

350 & 440—Dialtone (beat frequency=90 Hz),

440 & 480—Ringback (beat frequency=40 Hz),

480 & 620—Busytone (beat frequency=120 Hz).

In the example above, it is noted that all component frequencies areabove the old/established “300 Hz” limit. In general, in someembodiments the reference tones may be selected from the same frequencyrange.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative structural and functional designs for asystem and a process for activity detection in a call path by monitoringphase-related information of signals along the call path through thedisclosed principles of the present invention. Thus, while particularembodiments and applications of the present invention have beenillustrated and described, it is to be understood that the invention isnot limited to the precise construction and components disclosed hereinand that various modifications, changes and variations which will beapparent to those skilled in the art may be made in the arrangement,operation and details of the method and apparatus of the presentinvention disclosed herein without departing from the spirit and scopeof the invention as defined in the appended claims.

What is claimed is:
 1. A method of detecting activity during a phone call, the method comprising: establishing a call path between a first party and a second party; adding a first reference tone of a first repetitive waveform to a first electrical signal from the first party to the second party via the call path during the phone call; receiving a second electrical signal from the second party to the first party via the call path during the phone call, the second electrical signal including a reflected tone of a second repetitive waveform, the second repetitive waveform representing the first reference tone reflected from the call path; and detecting change in a phase difference between the first reference tone in the first electrical signal and the reflected tone in the second electrical signal during the phone call to detect a three-way call attempt or a call transfer attempt.
 2. The method of claim 1, wherein detecting the change in the phase difference comprises determining a zero crossing of the reflected tone.
 3. The method of claim 1, wherein the frequency of the first reference tone is fixed.
 4. The method of claim 1, further comprising adding a second reference tone in the first electrical signal, the second reference tone in combination with the first electrical signal generating a first envelope in the first electrical signal and a second envelope in the reflected tone.
 5. A method of detecting activity during a phone call, the method comprising: establishing a call path between a first party and a second party; adding a first reference tone of a first repetitive waveform to a first electrical signal from the first party to the second party via the call path; adding a second reference tone to the first electrical signal of a second repetitive waveform, the second reference tone in conjunction with the first reference to generating a first tone envelope in the first electrical signal; receiving a second electrical signal from the second party to the first party via the call path, the second electrical signal including a second tone envelope including a third repetitive waveform, the second tone envelope representing the first tone envelope reflected from the call path; and detecting change in a phase difference between the first tone envelope in the first electrical signal and the second tone envelope in the second electrical signal.
 6. The method of claim 5, wherein detecting the change in the phase difference comprises comparing inflection points of the first tone envelope and the second tone envelope.
 7. The method of claim 5, wherein detecting the change in the phase difference comprises comparing one of minimum reference points and maximum reference points in the first tone envelope and the second tone envelope.
 8. The method of claim 5, wherein detecting the change in the phase difference comprises analyzing zero crossings of the first tone envelope and the second tone envelope.
 9. The method of claim 5, wherein the frequency of the first reference tone is fixed.
 10. A system for detecting activity during a phone call, the system comprising: a reference tone generator configured to generate a first reference tone of a first repetitive waveform during the phone call; a summing module configured to add the first reference tone to a first electrical signal from a first party to a second party via an established call path during the phone call; an interface configured to receive a second electrical signal from the second party to the first party via the call path during the phone call, the second electrical signal including a reflected tone of a second repetitive waveform, the second repetitive waveform representing the first reference tone reflected from the call path; and a detection module configured to determine a change in a phase difference between the first reference tone in the first electrical signal and the reflected tone in the second electrical signal during the phone call to detect a three-way call attempt or a call transfer attempt.
 11. The system of claim 10, wherein the reference tone generator is further configured to generate a second reference tone, the summing module is further configured to add the second reference tone to the first electrical signal to generate a first tone envelope.
 12. The system of claim 10, wherein the first reference tone is between 150 and 600 Hz.
 13. The system of claim 10, wherein the phase difference is detected by a zero crossing of the first reflected tone and a zero crossing of the reflected tone.
 14. The system of claim 10, wherein the phase difference is determined by comparing inflection points of the first reference tone and the reflected tone.
 15. The system of claim 10, wherein the phase difference is determined by comparing one of minimum reference points and maximum reference points in the first reference tone and the reflected tone.
 16. The system of claim 10, wherein the phase difference is determined by comparing one of zero crossings, minimum reference points, and maximum reference points of the first reference tone and one of zero crossings, minimum reference points, and maximum reference points of the reflected tone. 